Such a filter device is used in water treatment facilities, wherein the filter is formed by an array of ceramic or polymer filter elements through which the raw water passes. When the pores of the filter elements after a period of use become blocked by filtered-out suspended matter in the treated water, a large volume of cleaning fluid is backwashed in a short time at a pressure of several bars (for instance up to 5 bar, depending on the strength of the filter element) in counter flow through the filter elements. Directing the cleaning fluid onto the filter elements will result in considerable head loss and an uneven distribution of the cleaning fluid across the filter elements. The resulting head loss and dynamic forces like water hammer can also lead to excessive forces on the filter elements and consequent damage.
The outlet and the cleaning duct can be formed by separate pipes but can also be combined. It is therefore an object of the present invention to provide a filter device having a cleaning duct supplying cleaning fluid at controlled outflow condition ensuring a reduced head loss and an even distribution of cleaning fluid across the filter elements.
It is another object to provide a filter device having a relatively small footprint. It is a further object to provide a filter device in which large volumes of cleaning fluid can be supplied to the filter in a short time at high pressures without the risk of water hammer.